1. Field of the Invention
The present invention relates to power transmission chains. More particularly, the present invention relates to silent chain, that is, power transmission chain comprised of interleaved sets of inverted tooth links, with the links being of asymmetrical construction.
2. Description of the Prior Art
Power transmission chains are widely used in the automotive industry. Such chains are utilized for ignition timing as well as for the transfer of power from the engine to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such a chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins or rocker joint pins, received in a pair of apertures. The links each have a pair of teeth or toes, which are defined by outside and inside flanks. The inside flanks of the toes are joined at a crotch.
The conventional power transmission chain drive comprises an endless chain of interleaved sets of links which is wrapped around two spaced sprockets supported on two generally parallel shafts. One of the shafts is typically the input shaft, which carries the driving sprocket, while the other shaft is the output shaft, which carries the driven sprocket. The links of the chain are adapted to fit over and about the teeth of the sprockets to enable the transmission of power from the input shaft and driving sprocket, through the chain, to the driven sprocket and output shaft.
Historically, silent chains have been constructed in which all of the links have the identical shape or configuration and all oriented in the same direction. Silent chains of more recent vintage generally are constructed of links which are all of identical configuration and are symmetrical. The links of such chains are generally of a contour having both inside flanks of the links being substantially straight or, alternatively, having both inside flanks of the links being of a convex curve. The construction of the inside flanks of such links can also include alternative configurations, such as having a portion being straight, a portion being curved, or varying radii of curvature along the inside flank. Differences in design can affect the operation of the link within the chain structure.
Power transmission chains have been used for many years in the automotive industry in both timing chain applications and power transfer applications. Chains having links with substantially straight inside flanks as well as chains having links with inside flanks of different configurations have been employed in these automotive applications. Historically, great care was taken in avoiding the mixing of these two types of links in chain assembly plants manufacturing both types of links. That is, great care was taken to produce chains with all links being of the identical type and configuration.
However, it was found that a mixture of links of two different inside flank configurations in a chain provided a chain that generated less noise when used in automotive applications than did some chains constructed of links of all identical configuration. A chain containing a mixture of links of two different configurations is described in U.S. Pat. No. 4,342,560, issued on Aug. 3, 1982. That prior art patent describes the concept of the mixture of sets of links with an inside flank of a first configuration with sets of links with an inside flank of a different configuration. Those different configurations can be achieved by varying the dimensions of the links as well as the flank shapes or the aperture locations.
The broad, generic concept of U.S. Pat. No. 4,342,560 was to change contacts between link flanks and sprockets by having differently configured link flanks in different sets of the chain. For example, in one species of the invention, some sets of links are comprised of links having at least one inside flank of a substantially straight configuration, while other sets of links are comprised of links having at least one inside flank of a different configuration. As the sprocket drives the chain, the sprocket teeth will contact the inside flanks of one configuration in one set of links, and will contact the inside flanks of another configuration in another set, or possibly the outside flanks of other links in the preceding set as a result of the different inside flank configuration at differing time intervals. Such differences alter or modify the contacts of the links with the sprocket.
In another species of the invention of U.S. Pat. No. 4,342,560, for example, some sets of links are comprised of so-called inside engagement type links and other sets of links are comprised of so-called outside engagement type links. The actual engagement of the links in such a chain is determined by the positioning of the sets of various types of links with respect to one another. Of course, the concept of U.S. Pat. No. 4,342,560 is broader than simply a combination of socalled inside engagement links and outside engagement links.
Thus, U.S. Pat. No. 4,342,560 is directed to the generic concept of noise reduction in a chain by providing a chain with the interspersing or mixing of links having a first inside flank configuration with links having an inside flank of a different configuration. Such a chain utilizes the noise reduction technique of attempting to modify the pattern of sound emanating from the chain contacting the sprocket by altering the types of configurations and thus altering the point and rhythm of contacts. Prior to U.S. Pat. No. 4,342,560, patents and structures taught and suggested the use of the driving links of the chain (as opposed to the guide links on the outside solely for the purpose of guiding the chain) of all identical inside flank configuration. The prior art did not teach or suggest the mixing of sets of links of a first inside flank configuration with sets of links of a different inside flank configuration together in the same chain assembly. Indeed, the prior art U.S. Pat. No. 3,377,875 to Sand and U.S. Pat. No. 3,495,468 to Griffel, both taught the modification of the sprocket teeth, rather than modification of the profile of the chain link flank, in order to modify the rhythm of the chain and sprocket contacts.
One advantage of using such a "hybrid" chain of two configurations of links is the avoidance of the need to modify the teeth of the sprocket. However, the two configurations of links must be kept separate during processing prior to assembly and then brought together to form the correct sets during manufacture. The optimal pattern of sets of links within the chain is determined prior to assembly and the separation of links prior to assembly is extremely important in order to achieve that pattern. As set forth in the U.S. Pat. Nos. 4,509,323 and 4,509,937, the outside upper surfaces of the links can be appropriately marked or identified by a shape in order to facilitate mixing of the links in proper positions during assembly.
The present invention is a species of the generic concept set forth in U.S. Pat. No. 4,342,560. The present invention overcomes the problem of separation by providing a chain formed of links all having the same overall outside contour. However, the links are asymmetrical in contour and are then given different orientations in the chain in order to provide the same result as the hybrid chain of U.S. Pat. No. 4,342,560. The links of U.S. Pat. No. 4,342,560 achieve that result by a link with a leading inside flank of a first configuration mixed with a link with a leading inside flank of a second configuration.
The links of the present invention are an asymmetrical combination of the two links of U.S. Pat. No. 4,342,560, which are oriented in two directions. Prior to assembly, when the links of the present invention are all oriented in the same direction, the links represent one link form. During and after assembly, the links comprise two links forms by virtue of their orientation in the claim assembly. In this manner, the links of the present invention perform the same function, contacting the sprocket in a random manner, in the same way, by having a link with a leading inside flank of a first configuration mixed with a link of a leading inside flank of a different configuration, to achieve the same result, modification of or altering of the chain and sprocket contacts. In the claims of both U.S. Pat. No. 4,342,560 and the present invention, the leading inside flank is modified by use of a different configuration of link or by orientation of the asymmetric link. Of course, in each case, the leading inside flank is the flank which primarily effects the link and sprocket contacts.